I think it depends on if you getting your room comped or not. If you're getting it comped, I'd absolutely stay in the GO Room. I find that Rio rooms are almost always free when I want to go to Vegas (even weekends) but I don't get a comped GO room option nearly as frequently.

Now, if you're PAYING for your room, I'd stay at Rio because I suspect the cost is cheaper than the GO room, as assuming you're kicking ass in the WSOP, why pay more money for a room you're not using?!?! Positive thoughts, right!?!!?!